Method of recovering magnesium scrap



Patented Jan. 19, 1943 2,308,938 METHOD OF RECOVERING MAGNESIUM SCRAP Vincent E. Shulnburg, Detroit, Mich.

No Drawing. Application August 29, 1941, Serial No. 408,890

3 Claims.

The present invention relates to a process of recovering fine magnesium scrap. v

A particular feature of the invention is that it provides for the recovery of very fine particles of magnesium which have hitherto been considered impractical to recover, because of their highly imfiammable nature, which makes it impossible to remelt them or dissolve them in a bath of molten magnesium.

According to the present invention these magnesium fines are recovered by stirring them into the surface of a bath of molten aluminum, or of an alloy consisting predominantly of aluminum.

Sincethe object is the recovery of the magnesium, the process is preferably continued until a magnesium-rich alloy is formed, which may be used in combination with other materials to produce commercial alloys containing aluminum and magnesium.

These, and other objects and advantage of the invention will become apparent as the description proceeds.

While preferred methods of carrying out the invention are disclosed herein, various changes may be made without departing -from' the spirit of the invention as herein set forth and claimed.

In fabricating parts from magnesium and its commercial alloys, a certain amount of scrap is produced. The larger pieces of scrap can be remelted or dissolved in a bath of the molten metal. However, some mechanical finishing operations produce very fine particles, such as sawings, turnings, borings, coarse filings, etc., which when subjected to such treatment, burst into flame and burn up completely. This is due to the fact that magnesium, when at its melting temperature, combines spontaneously with oxygen. Because of this inherent characteristic of these magnesium fines, they have not in the past been recovered.

I have discovered that these magnesiumfines may be recovered by stirring them into the surface of a bath of molten aluminum, or of an alloy consisting predominantly of aluminum, without combustion nesium. In this manner nesium alloy is formed that is useful for many purposes.

I believe that one explanation of the fact that these magnesium fines can be thus melted in aluminum is that aluminum has a higher rate of thermal conductivity then magnesium and freezes very rapidly when it contacts a cool surface. Hence the molten aluminum covers the magnesium particles and immediately chills to form a protective coating that prevents combustion of the magnesium.

Another advantage of the process applies particularly to scrap resulting from the finishing of magnesium castings. Such castings, when made in sand molts, inevitably contain some foundry sand. When placed in molten magnesium this sand reacts chemically with the magnesium to release gases which cause porosity when the melt is cast. But molten aluminum does not react with the sand, and thence magnesium fines containing sand canbe melted in aluminum, the sand being later removed with the impurities.

Since the object of the process is the recovery of magnesium, the higher the percentage of magnesium in the resulting alloy, the greater the economy of operation. However, I have found that approximately 50% of magnesium in the alloy is the top limit, since beyond that point the molten bath increases in volume, apparently due to the formation of gas within the mass, and the poured metal becomes brittle. In fact, I have found approximately 35% of magnesium to be the top practical limit.

An aluminum-magnesium alloy having such a high percentage of magnesium is not a commercial alloy, but it serves as a hardener alloy, that is, as a vehicle to introduce magnesium into aluminum alloys or aluminum into magnesium alloys.

The process is applicable to magnesium alloys as well as to pure magnesium, all of which are referred to herein as magnesium material. Similarly the molten bath may be aluminum alloy as well as pure aluminum, all of which are herein called aluminum material.

The fine particles of scrap may be given preliminary treatment to facilitate the process, such as briquetting them for convenient handling.

I claim:

1. The process which comprises stirring into a molten bath of aluminum material particles of magnesium material so small that they burn up when placed in molten magnesium.

2. The process which comprises stirring into a molten bath of aluminum material fine particles of magnesium material so small that they burn up when placed in molten magnesium, and continuing the addition of the magnesium material until the bath contains approximately 35% of magnesium, thereby producing an aluminummagnesium hardening alloy.

3. The process which comprises stirring into a molten bath of aluminum material particles of silicon-containing magnesium material so small that they burn up nesium.

VINCENT E. SHULNBURG.

when placed in molten mag-- 

